1. Field of the Invention
The present invention generally relates to living tissue stimulators and, more particularly, to a programmable living tissue stimulator.
2. Description of the Prior Art
Various devices are presently in existence which are implantable in a human patient to stimulate body tissues. Among the best known of these devices is the cardiac pacemaker, which provides stimulating pulses to a patient's heart, via one or more electrodes, connected to the pacemaker through electrode leads. Many of the existing implantable cardiac pacemakers include a power source in the form of a battery, which is rechargeable by means of recharging power, transmitted to the implanted pacemaker from an external power source.
In recent years extensive research has been directed to develop stimulators for other than the heart, in order to relieve patients of the crippling effects of various physiological disorders. For example stimulators have been proposed to stimulate the brain, the spine, muscles, glands and organs or any other stimulatable matter. The stimulating pulses from these stimulators are intended to help patients, suffering from various disorders, e.g. cerebral palsy, spasticity, rigidity, epilepsy and other disorders, which are due to either improper, or the absence of natural stimulating pulses. Also, it has been appreciated that pain, such as phantom limb pain, resulting from a severed limb may be alleviated by applying stimulating pulses to the nerves proximal the damaged area. A workshop was held at the National Institute of Health, Bethesda, Maryland on Apr. 27-28, 1972, and a report of the workship entitled "Functional Neuromuscular Stimulation" was published in 1972 by the National Academy of Sciences, Washington, D.C.
Different disorders require different stimulations. That is, the various parameters of the stimulating pulses, such as pulse amplitude, pulse frequency, pulse width, and other pulse parameters have to be different for different disorders and may differ from patient to patient. Furthermore, even for the same patient, the parameters may have to be varied depending on the patient's condition at any given time. Clearly, it would be prohibitively expensive to fabricate a customized stimulator for each patient. Furthermore, even if tailor-made for a specific patient, the stimulator would have to be capable of varying the pulses' parameters in order to vary the stimulation to suit the patient's changing conditions. Also, in a stimulator designed to stimulate tissue at different locations in the body, e.g., the right and left hemispheres of the brain, it is important to be able to control the relationships between the pulses to be applied to the different brain portions.
The only practical solution to the problem is to provide a basic implanted stimulator system, hereinafter referred to as a human tissue stimulator (HTS), which is programmable, in response to signals which are transmitted to the HTS from a source external to the body, in order to vary the parameters of the pulses which the HTS is to provide, to suit the needs of each particular patient depending on his type and state of disorder. Since the patient's safety is paramount, it is obvious, that the programmable HTS must be extremely reliable. Also, it is very important to provide the programmer, e.g. a doctor, with an accurate indication of the parameters which were introduced into the HTS in order to verify that the proper parameters were accepted. Also in many cases it is desirable to observe the biological response to a stimulation by measuring the electrical potential produced by the tissues being stimulated.
Since we live in an environment which is noisy, i.e., one in which spurious electrical and other type signals, generally referred to as noise are present, it is extremely important that the signals which are transmitted to the implanted HTS to program it, in order to vary the parameters of the pulses provided thereby, are not affected or altered by the noise, and that, if affected the affected signals received by the HTS, do not cause improper pulse parameters, which, if permitted to be introduced and stored in the HTS may endanger the patient's life, particularly when stimulation takes place at such extremely sensitive parts of the body as the brain or the spine. Quite often a doctor after examining a patient may wish to change one or more of the parameters, e.g., pulse amplitude and not disturb the other parameters. Also, it is believed desirable to enable the patient himself to vary one or more selected parameters, if and when such variation is necessary, when the patient is away from the doctor's office. This capability may be desirable in order to alleviate unexpected discomfort or pain, as a result of the stimulating pulses and/or increase the stimulation when it is felt to be needed.
None of the known human tissue stimulators, which have been proposed to date, possess the desired capabilities as hereinbefore discussed. In the known stimulators, proposed to date, all parameters must be changed even when less than all of the parameters require change. Also, in most systems only the doctor can change the parameters, and even the doctor is not provided with a direct indication of the parameters introduced by him into the stimulator. Rather, the indication of the introduced parameters is provided indirectly, by recording or otherwise observing the response of the patient to the stimulating pulses, which are produced by the stimulator as a result of the doctor-introduced parameters. Furthermore, in the prior art during programming of the stimulator, the patient has to be practically in contact with the external programming unit, from which the programming signals are transmitted to the implanted stimulator, in order to minimize the effect of the ever-present noise. The patient cannot move about during programming and/or be at an appreciable distance, e.g., several feet, from the programming unit, which under some circumstances would be most desirable. For example, correcting a gait dysfunction by stimulating a nerve to a leg muscle to produce a normal walking motion.